Effect of E4031, a class III antiarrhythmic drug, on ischemia- and reperfusion-induced arrhythmias in isolated rat hearts

The delayed outward rectifier K⁺ channel has a role in the increase in automaticity of myocytes under pathophysiological conditions. The purpose of the present study was to clarify the effect of blockade of outward recitifier K⁺ channels by a class III antiarrhythmic drug, E4031, on ischemia- and reperfusion-induced arrhythmias. Ion fluxes, energy metabolites and cardiac function were measured and the epicardial electrocardiograms of Langendorff-perfused rat hearts were recorded during initial perfusion, global or regional ischemia and reperfusion. 10^-7 M of E4031 administered during the initial perfusion did not prolong the QT interval, but slowed the heart rate (Control: 222, E4031: 183 bpm, p < 0.05), increased myocardial ⁴⁵Ca²⁺ uptake (Control: 2.1, E4031: 2.9 μmol/g dwt, p < 0.05) and attenuated the loss of intracellular K⁺ during ischemia (Control: 238, E4031: 248 μmol/g dwt, P < 0.05). E4031 tended to reduce ischemia-induced ventricular tachyarrhythmias (Control: 60, E4031: 30%, n.s.), but reperfusion-induced ventricular tachyarrhythmias were sustained longer by the administration of E4031 (Control: 255, E4031: 623 sec, p < 0.05). Prior exposure to E4031 decreased the depletion of high energy phosphates during ischemia, but suppressed their recovery during reperfusion. These results suggest that the attenuated loss of K⁺ from the ischemic myocardium and the decrease in heart rate by E4031 contributed to the reduction of ischemia-induced arrhythmias. However, the increase in myocardial Ca²⁺ uptake and altered energy metabolism may be responsible for the increase in reperfusion-induced arrhythmias.